Owing to the conditions that a lot of sorts of portable terminals have functions of image processing, especially the functions of digital camera, there is a great need for massive data transmission. A portable terminal with a built-in digital camera is capable of recording still images and moving images and accordingly methods for transmitting such image data to the outside have been in demand. A method generally used at present is to attach image data to e-mails.
As the number of pixels per picture increases, however, data volume of one image has extremely increased and, therefore, the above method to transmit image data for another units by attaching the data to e-mail causes overloads of networks and also the communication costs are mounted up to the large sum.
Although it is possible to easily obtain high-speed transmission using a wired communication system, this system is rather inconvenient for everyday use because it is time-consuming and troublesome to connect signal lines before you start transmission and in addition you are required to carry signal cables suitable for both of your own unit and the other party's unit all the time.